Scott Johnston, most recently COO at high-speed trading firm Tower Research Capital, is to take on the same role at Citadel Securities in April 2017, according to people familiar with the matter.

He will report to Kevin Turner, the former top Microsoft executive who became Citadel Securities' CEO in July this year.

Citadel established a separate market-making unit in 2002 and it has become one of the biggest participants in the global equities, futures and options markets.

In recent years, it has also expanded into the fixed-income markets traditionally dominated by dealers, such as interest-rate swaps, credit derivatives and US treasuries.

As a non-bank market-maker, it has been able to avoid new capital rules that have crimped the activities of banks. At the same time, it has benefited from post-crisis rules forcing swaps onto electronic trading platforms and through clearing houses.

The 2010 Dodd-Frank Act implemented many of those changes in the US, where Citadel Securities says it is now among the top three firms for US dollar interest-rate swaps traded on Bloomberg by value.

It is beginning to replicate that presence in Europe, where similar post-crisis reforms are only just beginning to take effect. It is now active on platforms operated by Bloomberg, Tradeweb and interdealer brokers in the region. It says it has a top 10 ranking in euro-denominated interest rate swaps on Bloomberg.

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Citadel Securities has hired several big-name executives in recent years, including UBS's Paul Hamill as global head of fixed, income, currencies and commodities and IMC's Remco Lenterman as global head of business development.

Johnston had been with Tower for more than seven years, and has previously held roles at CME Group, UBS and options trading firm O'Connor & Associates. He left Tower in late October, according to his LinkedIn page.

CORRECTION: This article has been updated to clarify that Johnston will join in April 2017.